Axial Skeleton

Introduction to Axial Skeleton

• Overview of the axial skeleton components:

  • Skull and mandibles

  • Vertebrae

  • Ribs

  • Sternum

  • Hyoid apparatus

Learning Goals

• Understand and describe key aspects of the canine axial skeleton,

  • Vertebral formula for dogs: C7 T13 L7 S3 Ca 20-23

  • Typical vertebra features: vertebral foramen, vertebral canal, and intervertebral foramen

  • Distinctions between cervical, thoracic, lumbar, sacral, and caudal vertebrae

  • Joints and ligaments associated with vertebrae

  • Rib articulation with vertebrae

  • Define axial muscles, including epaxial and hypaxial, and their locations/functions

Vertebral Formula in Dogs

• General composition of the dog’s vertebral formula:

  • 7 cervical (C)

  • 13 thoracic (T)

  • 7 lumbar (L)

  • 3 sacral (S)

  • 20-23 caudal (Ca)

Features of a Typical Vertebra

• Components of a vertebra:

  • Vertebral body: site of intervertebral discs between adjacent bodies

  • Vertebral arch: made of pedicles (walls) and laminae (roof)

  • Processes:

    • Dorsal spinous process

    • Transverse (bilateral) processes

    • Articular processes (cranial and caudal pairs)

Vertebral Canals and Foramina

• Vertebral Canal:

  • Formed by vertebral foramina; houses the spinal cord

• Intervertebral Foramen:

  • Found laterally between adjacent vertebrae;

  • Contains spinal nerves and blood vessels

Cervical Vertebrae: Atlas and Axis

• C1 (Atlas):

  • Unique characteristics: large transverse processes (wings) and no spinous process

• C2 (Axis):

  • Prominent spinous process and dens that articulates with the atlas

Joints Associated with the Atlas

• Atlanto-occipital Joint:

  • Joint between the occipital condyles of the skull and Atlas (C1)

  • Allows nodding (yes joint)

• Atlantoaxial Joint:

  • Joint between Atlas (C1) and Axis (C2)

  • Allows for rotation (no joint)

Ligaments of the Atlas and Axis

• Transverse Ligament of the Atlas:

  • Stabilizes the dens against the atlas

Cervical Vertebrae C3-C6

• Characteristics:

  • More typical than C1 and C2

  • Short spinous processes

  • Transverse foramen present (C1-C6) for vertebral artery, vein, nerve

• C7:

  • Lacks transverse foramen but has a costal fovea for rib articulation

Thoracic Vertebrae

• Features:

  • Long spinous processes and shorter transverse processes due to rib articulation

  • Costal foveae for rib articulation on the bodies and transverse processes

Ribs and Sternum

• Dog has 13 pairs of ribs and 8 sternebrae.

  • Costochondral junction and costal cartilage noted

Flat Chested Kitten Syndrome

• Characterization: thoracic deformity with an angulation at costochondral junction leading to a flattened rib cage configuration

Rib Articulation with Vertebrae

• Head of each rib articulates with the body of the corresponding thoracic vertebra.

  • For ribs 1-10, they also articulate with the body of the cranial vertebra.

  • Tubercle of each rib articulates with the transverse process of its corresponding vertebra.

Lumbar Vertebrae

• Characteristics:

  • Large bodies, large transverse processes, prominent spinous processes.

Sacrum

• Fusion of S1, S2, S3 vertebrae;

  • Articulates with ilium;

  • Sacral foramen for nerves instead of intervertebral foramina.

Caudal/Coccygeal Vertebrae

• First few resemble typical vertebrae; become more rod-shaped onward.

  • Hemal arch on Ca4-Ca6 to protect tail vessels.

Intervertebral Discs

• Structure:

  • Two parts:

    • Anulus fibrosus: outer collagenous fibers, thicker ventrally.

    • Nucleus pulposus: inner gelatinous core;

  • Function: shock absorber, evenly spreading the load between bones.

Intervertebral Disc Disease

• Types: Acute and chronic; potential spinal cord compression.

Vertebral Ligaments

• Supraspinous Ligament:

  • Extends dorsally along spinous processes of T1 – Ca3 vertebrae.

• Nuchal Ligament:

  • Cranial extension of the supraspinous ligament, courses between spinous processes of the axis (C2) and T1; absent in cats and pigs.

Conclusion

• Recap of the axial skeleton components and significant anatomical features for efficient veterinary practice.